Which is the best material for tensile structure

Which is the best material for tensile structure

While it is widely known that tensile structure has many advantages over a conventional brick and concrete structure, what we seldom doesn’t give heed is to the materials used in the fabrication of tensile membrane – the building block of tensile structure. In this article we will look at some common tensile membrane materials.

Tensile membrane made from polymers or fiber coated polymers is the building block of any tensile structure. But is there any single most fabric which can be termed to be the best? The answer is no. It must be understood that the uniqueness offered by a tensile structure is but a product of the exceptional quality of the tensile membrane used in its construction. In this article, we look at various materials used as tensile fabric. We will also try to know about their properties in detail. But before that we must be aware about the structure of a tensile membrane. These fabrics could be either single layered, double-layered or multi-layered. It all depends on its intended use. A typical multi-layered tensile membrane looks like the one shown below. It must be noted that it’s not mandatory to provide each layer shown in the image below. It’s just a representational image.

1. Ethylene Tetrafluoroethylene (ETFE)

Originally developed by DuPont in 1980s, ETFE is a fluorine based plastic which was used as an inert coating in aerospace industries thanks to its mechanical toughness. Due to its greenhouse properties, it increasingly found its use in agricultural sector and as coating of solar cells. With time, it has widened its scope and presently is widely regarded as the premium material for transparent cladding applications. Perhaps the best testimony to its versatility and popularity is the Beijing National aquatic center.

ETFE tensile membrane can be used as a single layered film supported by wire cables or aluminum or LW steel to maintain its distinctive shape and grant stability. When used in its double-layered form, it incorporates a pneumatic system which helps it to maintain a column of air between the films. These inflated cushion shaped structure can be filled with low pressure air to grant it exceptional thermal insulation and stability against winds and snow.

No end to benefits

You may be thinking. So, why is ETFE tensile membrane so much in use? The reason is the host of benefits that it offers vis-à-vis traditional construction materials. Most of the benefits mentioned below is common to almost every tensile structure. In addition, ETFE has its own special advantages as well. Let’s see some of this benefits.

Durability – the ETFE film is resistant to most of the vagaries of nature. Like many other tensile membrane, it is extremely abhorrent towards harsh chemicals and extreme temperature variations. Furthermore, ETFE has this unique quality of being resistant to pollutants and UV rays as well. All of this not just enhances its life but also minimizes the extent of maintenance that it needs.

Light transmission par excellence – it is exceptionally good at allowing light to transmit through it. Almost 90-95% of the light falling upon it is able to get to the other side. Combine this with its capability to allow UV rays to propagate through it and what you get is an excellent greenhouse material, tailor made for plant growths.

Elastic – ETFE tensile membrane is blessed with an exceptionally good tensile strength and its elongation at break is almost 100-350% which is quite impressive. All this values impart excellent elasticity to ETFE. So, if you are thinking of stretching your car parking tensile structure to include your two-wheeler as well, do it without any hesitation.

Visually appealing – ETFE based tensile structure is known for its elegance and jaw dropping design. There’s no dearth of testimony to justify it. The famous ‘water-bubble’ aquatics center in Beijing (below) or the Lamezia stadium in Calabria (above) is just two of the many examples of buildings made from ETFE.

Environmentally sustainable and sound – if there’s anything ‘green’ in construction, its ETFE tensile membrane. And it’s not just the color we are talking about but its environmental value as well. It is energy efficient, recyclable and sustainable. Every stage of manufacturing – from extrusion to transportation uses very little energy in comparison to other cladding material, thus reducing its carbon footprint. The ETFE tensile membrane can also be recycled once discarded. This not just reduces the amount of energy needed in restructuring but also reduces the energy demand for waste management.

Good for your pocket – thanks to its properties mentioned above, tensile structure constructed from ETFE tensile membrane is very cost-effective. It saves a lot of money on lighting, construction, installation and maintenance. So, if you are not in a position to spare much, try them out.

Along with this, ETFE also exhibits exceptional flame retardant property and ability to get integrated with photovoltaic cells to meet performance and aesthetic standards. You can read more about the properties of ETFE here.

Maintenance sans hassle

ETFE films have these unique ‘self-cleansing’ properties that do not allow dirt, dust and debris to stick onto its surface. But despite these qualities, a regular inspection is required to find and fix some mechanical issues like filter replacements, air inflation etc. This will help a lot in extending the life of these tensile structures.

2. Polytetraflouro ethylene (PTFE) fiberglass

Since its accidental discovery by Roy Plunkett for DuPont in 1938, PTFE or Teflon coated fiberglass has found wide usage in aerospace and computer applications mostly for wiring as hookup wires, coaxial cables etc. But, of late, it is being used as a tensile membrane for construction of tensile structure thanks to its extreme durability and weather resistance. One of its application can be seen in the construction of Rhine Gallery, a shopping center in Ludwigshafen, Germany.

PTFE is used around the globe as the preferred material for large-scale permanent or semi-permanent tensile structure. Its elasticity and versatility makes compliance to specific construction codes much easier. TiO2 coated PTFE is a flame resistant tensile membrane that appears like a green leaf of a tree, providing shade and neutralizing pollutants and odors at the same time. PTFE is also thought to perform exceptionally well as an acoustic liner providing short reverberation time.

Advantages galore!

Exceptionally high elasticity – flexibility imparts robustness to PTFE tensile membranes. This is of great help in designing complex structures. Its elasticity emanates from its high ultimate tensile strength (about 500,000 PSI). So, stretching your PTFE based awning a bit to cover your patio and courtyard shouldn’t concern you much.

Light transmission – it reflects almost 68-75% of light incident on its surface and the ones that get transmitted through it are color balanced, diffused and devoid of shadow and glares. The tensile structure made from PTFE are energy efficient as well due to their ability to utilize daylight brightness. Its shading coefficient (also called as solar heat gain coefficient) of 14-28% helps save energy in cooler climates with high lighting levels and in warmer climate with low lighting levels. And this gain is much more in comparison to conventional glazed panel structures.

Longevity – if there’s one thing that PTFE is famous for, it is its exceptionally long life. An average PTFE tensile membrane is expected to last almost 25 years. Of course, it can be extended by regular maintenance. A PTFE-coating is also resistant to corrosion, friction and wear-n-tear which greatly enhances its durability.

Chemical resistance – it also exhibits inertness to large number of chemicals. This finds use in construction of buildings that are in close proximity to chemical hazards like industries. See table below.

Weather resistant – apart from durability, the second most striking feature of a PTFE tensile membrane is its resistance to elements of nature and abhorrence to oil and water. This is partly due to its inert chemical nature. The resistance to UV radiation also slows down the rate of degradation thus extending the already long life.

Cost effective and sustainable – With so much to offer it’s only rational that a tensile structure constructed from PTFE be cost effective. Like other tensile membrane, it can also be recycled and reused in one way or the other. Its long life and frugal maintenance bill also drives the cost down. You can learn more about PTFE tensile membrane here

Maintenance

Its maintenance can be done in the same way as other tensile membrane. It could be either done manually or with automatic sweepers. Unlike ETFE, PTFE is not known for its self-cleansing property, hence regular maintenance and inspection is essential.

3. Polyvinyl chloride (PVC) or Polyvinyl dine fluoride (PVDF)

The world’s third most widely produced synthetic plastic polymer is an excellent alternative to the time-honored roofing systems made of brick and cement. To extend its durability, Polyvinyl chloride or PVC membrane is usually coated with acrylic or PVDF (polyvinylidene fluoride). Accidently discovered by Eugen Baumann in 1872, it was not until mid-1960s that PVC actually found its use as a construction material, thanks to the discovery and production of PVDF and Acrylic fibers. Read here to know more about PVDF.

Produced in a multitude of colors, PVC is an excellent substitute for ceilings. It is being used widely to construct what is commonly known as false ceilings. The bright and white colored PVC tensile membrane reduces radiant heat gain, keeping interiors cooler even during warmer conditions. Sometimes it is coated with TiO2 that imparts it flame retardant capabilities. Of late, there use has been increasingly rapidly. One of the best examples of building constructed using PVC is National Performance Center for Sport, Scotland.

Benefits in abundance!

Strong and lightweight – With high tensile strength, resistance to abrasion and light weight, it’s no wonder why they are so much in demand. Any tensile membrane which is to be used as roofing material must be strong and light. The PVC meets the requirement perfectly.

Easy installation – The tensile fabrics made from PVC can be easily cut, shaped and welded. This assists a lot in its prefabrication. Even during installation, it is extremely easy to handle and assemble.

Durability – When coated with acrylic or PVDF, the durability of tensile structure made from PVC tensile membrane can be easily extended to 15-20 years. This is largely possible due to the exceptional resilience offered by these fibers and polymers to weather elements. Even if the structure is exposed to high UV rays, the decrement is not that significant. It still clocks about 10-15 years.

Say no to flame, electric shocks and extreme weather – PVC especially the ones coated with Titanium oxide, acrylic and PVDF are very effective against flame, extreme weather elements like rain, snow, UV and harsh sunlight. They also provide good insulation against electric shocks.

Cost-effective – the tensile membrane composed of PVC is strong, weather resistant, elegant and available in different shades and color. It is also very easy to fabricate, design and assemble.

Safe material – many believe that association of PVC with TiO2 will turn it toxic. But that is not true. They are absolutely safe and are being used extensively as well. TiO2 is important to impart additional flame retardant capabilities.

Versatile – Thanks to its respectable elongation value of 20-50%, PVC is very amenable to be used in variety of shapes and designs. It also gives a high degree of freedom to architects to develop new structures.

Maintenance

PVC usually forms a mesh like fabric. This can be turned solid like thermoplastics or can be used in their elastic state. In either ways, regular maintenance is necessary. While PVDF coating does provides it with some self-cleaning ability, the acrylic fibers are too obtuse towards dirt and dusts. The solid ones can be easily cleaned manually, but the elastic ones are better suited for automatic cleaning techniques.

4. Other notable tensile membranes

While the three above are most widely used in construction of tensile structures, there’re few others as well. These too have been rising in prominence. With innovation, there demand is only going to rise. We will look at some of them.

Tensotherm – insulated tensioned membrane

Developed by Geiger Engineers in 2008, tenso therm is a translucent and insulated composite tensile membrane comprised of PTFE fiberglass exterior skin and acoustic interior liner. It has this exceptional quality of allowing sunlight to pass through it and providing diffused, glare-free daylight. Due to the presence of aerogel filled blankets between outer and inner PTFE liners, it is very effective in providing thermal insulation. It is same as your woolen blanket. They are durable as well.

ePTFE

It is a PTFE based high translucent material known for its exceptional aesthetics and durability. Compared to PVC, ePTFE transmits almost 40% of the light incident on it. Its ability to disperse light evenly makes it a great tensile membrane for use in malls and office spaces. It is also very useful for designing tensile structures for housing indoor plantations.

Polychlorotrifluoro ethylene (PCTFE)

It has similar properties like other fluorine based polymerssuch as PTFE, FEP etc. but has more to offer in terms of mechanical rigidity (in comparison to others). It has high compressive strength, low deformation, mechanical stability under high temperature and chemical conditions. You can read more about them here.

In a nutshell…

There’s no single tensile membrane which can meet to all requirements and be used in all circumstances. After reading this article, we hope that it helps you a bit in searching and finalizing the best tensile membrane for your tensile structure. Once you are done choosing, visit here (‘step-by-step guide to build a tensile structure’ article here) to know how you can design a tensile structure, step-by-step. To summarize, see the table below to get a rough idea of where different tensile membrane materials stand on different properties.